Abstract

We use cross-sectional transmission electron microscopy to study the damage induced below the surface of indium phosphide(InP) samples by single and multiple femtosecond laser pulses with a photon energy lower than the InP band gap. Single-pulse irradiation creates a deep crater with a resolidified surface layer consisting of quasiamorphous indium phosphide. The resolidified layer has a thickness of at the center and extends laterally beyond the edge of the crater rim. Exposure to multiple femtosecond pulses of 2050 nm center wavelength results in the formation of laser-induced periodic surface structures (LIPSS) with two different periods, one () less than but close to the laser wavelength and one () four times smaller. Segregation beneath both types of ripples leads to the formation of In-rich particles embedded in the resolidified surface layer. Extended defects are detected only below the center of the multiple-pulse crater and their distribution appears to be correlated with the LIPSS modulation. Finally, LIPSS formation is discussed in terms of the observed subsurface microstructures.

Received 30 July 2006Accepted 30 October 2006Published online 09 February 2007

Acknowledgments:

We are grateful to Professor David Embury, Travis Crawford, and Jörn Bonse for helpful discussions. We thank Andy Duft for the AFM imaging and Mike Phaneuf for the discussion on FIB sample preparation. We would like to acknowledge the support from NSERC (Canada), MMO (Ontario), CFI (Canada), and OIT (Ontario). We are grateful to Fred Pearson and Andy Duft for technical support and maintenance of the facilities. One of the authors (M.C.) acknowledges support from a NSERC postdoctoral fellowship.